Study Tracks Commute Times: How Does Your City Compare?
"The report is part of the American Community Survey, a sampling of selected households that the Census Bureau conducts every year. It asked respondents for the length of their daily trip to work. The average San Francisco commute was 29.2 minutes -- second-longest among cities over 250,000 in California behind Riverside, which averaged a 29. 8 minute trip."
Thanks to C. Scott Smith